1. Field of the Invention
The present invention relates to an apparatus and method for converting groove/land polarity, and especially in an apparatus and method capable of toggling a reliable and exact groove/land polarity upon determination of a groove/land track change on an optical medium.
2. Description of the Related Art
Recently, various types of disk-shaped optical medium with high-density capacity was progressively developed in compliance with trends of accommodating huge amounts of digital contents, for instance, video or audio data. For one kind of disk-shaped optical medium such as DVD±RW, the data is recorded by a pickup head of a recording/reading device in grooves as pits formed on the surface of the optical medium. For another kind of disk-shaped optical medium such as DVD-RAM (Digital Versatile Disk-Random Access Memory), the data is successively allocated and recorded by a pickup head in both grooves and lands as different-layer pits formed on the surface of the optical medium. Such a groove/land track on the optical medium is divided into specific number of sectors each containing an embossed header data region and a user data region. The embossed header data region prerecords a physical identification data (PID) with reference to physical layout of the sector where the embossed header data region is located. Each sector owns its physical identification data (PID) independent of the other sectors. As soon as an alternation of land and groove tracks, i.e. a track changing position from a groove to a land or vice versa, is scanned by a beam spot of the pickup head during a reading/writing process on the optical medium, a track converting signal responsive to the track change is generated to enable a servo unit of the reading/writing device to toggle a groove/land polarity (phase) of an output control thereby reliably reading/writing data from or onto the optical medium.
Thus, it is a great topic of interest in how to determine a groove/land changing position on the optical medium to ensure a stable servo control during each recording/reading process on the optical medium.
A prior art disclosed in an U.S. Pat. No. 6,091,678 specifies that a tracking error signal (also called a “high frequency push-pull” or “HPP” signal) is generated to decide a polarity of the header field (plus or minus) responsive to a groove/land track change on an optical medium. Then a groove/land polarity toggle point 12 (as shown in FIG. 1b) will be determined upon occurrence of a phase difference resulted from the polarity change of an envelope signal. For example shown in FIG. 1a, a cycle 10 of an envelope signal has a 180-degree phase difference relative to the previous cycle 6. However, the envelope signal is often unstable to be detected during slice and therefore is insufficient to determine the groove/land polarity toggle point.
Another prior art disclosed in an U.S. Pat. No. 6,333,902 specifies that a groove/land changing position can be determined by counting down a total number of sectors to find the last sector at an end of a track wherein the number of sectors can be counted by counting cycles of the wobble signal since the wobble exists in each sector. Alternatively, the U.S. Pat. No. 6,333,902 further specifies that a groove/land changing position can be determined by finding out a bit value of physical identification data relative to any one of the last 3 sequent sectors at an end of a track. However, as long as the physical identification data of the last 3 sectors in each track all fails to be decoded, the mechanism also fails to determine an exact groove/land changing position.
To address the foregoing drawbacks, it is, therefore, a primary objective of the present invention to provide an apparatus and method for converting a groove/land polarity upon determination of a groove/land track change on an optical medium, which merely needs to initially find out a reference groove/land changing point on the optical medium, or pick up any one decoded physical identification data (PID) on the optical medium, and then is cable of timely and determining the next groove/land changing points for converting groove/land polarity, even all of the next track changing points distributed on the optical medium, especially for one kind of optical medium which has to use an exact groove/land information to perform a stable servo control. Also, the present invention needs not to decode the last sectors for finding out each one of the groove/land changing points on the optical medium.
It is a secondary objective of the present invention to provide an apparatus and method for converting a groove/land polarity upon determination of a groove/land track change on an optical medium, which merely needs to initially find out a relationship between a first PID value of a first sector decoded and a second PID value of either a second sector provided or a reference groove/land changing point formed on the optical medium, and then is cable of timely and determining each of oncoming groove/land changing points on the optical medium for converting the groove/land polarity.
To achieve the aforementioned objectives, a first embodiment of the present invention introduces an apparatus for determining a groove/land polarity upon a groove/land track change on an optical medium, which includes a reference groove/land detector, a sector information unit, a sector counter, a comparator and a groove/land toggling unit. Meanwhile, the reference groove/land detector is operative to initially detect a reference groove/land changing point in a zone of the optical medium. The sector information unit as a lookup table pre-stores some sector information relative to the optical medium, thereby providing a first value indicating a total number of sectors per track based on the detected zone on the optical medium. The sector counter is operative to count a number of sectors per a predetermined cycle, from the reference groove/land changing point to approach a subsequent groove/land changing point along a track where the reference groove/land changing point belongs, and the number of sectors counted per the predetermined cycle is treated to be a second value. The comparator compares the first value with the second value to determine whether the subsequent groove/land changing point occurs on the optical medium or not. While the first value is found identical with the second value, the groove/land polarity conversion is performed at a header.
Furthermore, a method for converting a groove/land polarity upon a groove/land track change on an optical medium is introduced as the following steps of:
detecting a reference groove/land changing point formed in a zone of the optical medium;
generating a first value indicating a total number of sectors per track according to the detected zone;
generating a second value by counting a number of sectors per a predetermined cycle, from the reference groove/land changing point to approach a subsequent groove/land changing point along a track where the reference groove/land changing point belongs;
comparing the first value with the second value per the predetermined cycle;
determining the subsequent groove/land changing point to toggle a groove/land polarity when the first value is found identical with the second value; and
After the subsequent groove/land changing point is determined, setting the second value to zero for re-generating the second value per the predetermined cycle by counting the number of sectors until the other oncoming groove/land changing points are determined one by one.
Moreover, another embodiment of the present invention introduces an apparatus for converting a groove/land polarity, which comprises a physical identification (PID) detector detecting a first sector from the optical medium into a first PID value, a sector information unit providing an information of at least one sector, including a second PID value indicative of either a second sector or a reference groove/land changing point laid on the optical medium, a sector counter counting a first value, an initiation of which is set by the sector information unit based on the at least one sector information and/or the PID detector based on the first PID value, and a comparing unit determining at least one of the oncoming groove/land changing points for performing the groove/land polarity conversion, based on when the first value approaches a second value either predetermined or generated by the sector information unit according to the at least one sector information.
Beside, a method for converting a groove/land polarity upon a groove/land track change on an optical medium is introduced as the following steps of:
detecting a first physical identification (PID) value indicating a physical layout of a first sector laid on the optical medium;
providing an information of at least one sector relative to the optical medium, including a second PID value indicative of either a second sector or a reference groove/land changing point laid on the optical medium;
counting a first value, wherein an initiation of the first value is generated based on the at least one sector information and/or the first PID value; and
determining at least one of the other groove/land changing points allocated on the optical medium for performing the groove/land polarity conversion, based on when the first value approaches a second value either predetermined or generated according to the at least one sector information.
These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings.